The present invention relates to methods and apparatus for roller type processing, which are suitably used for hemming a peripheral edge, e.g. a door panel, hood panel or the like for a vehicle, or for general bending processes.
As shown in FIG. 18, the applicant has proposed a roller type processing apparatus M for processing a portion We to be processed by roll-pressing a roller r0 along the peripheral edge of the portion We of a workpiece W (as disclosed in Japanese Patent No. 1844282).
This roller type processing apparatus M has a robot arm R to which a roller is attached and which can be moved according to a predetermined operating program, which permits the roller r0 to be roll-pressed along a desired travelling path. As a result, smooth processing along a curved contour can be achieved. Thus, the apparatus M can be suitably used, in particular to hem a workpiece, such as a door panel or an engine hood panel of a vehicle.
Further, the travelling path of the robot arm R can be changed by changing the operating program of the robot arm R, thus generally providing greater versatility compared to conventional processing using pressing dies.
However, the above prior art apparatus M was found to have some disadvantages. As a specific example, for this hemming process, it is difficult to completely bend the workpiece portion We in one pass using the roller r0. Therefore, according to the prior art, the workpiece portion We is first bent by about 45xc2x0 with the roller r0 being held in a position tilted by about 45xc2x0 (a pre-bending process or an intermediate bending process). Thereafter, the position of the roller r0 is shifted to a horizontal position. The roller r0 held in the horizontal position is again roll-pressed along the portion We that has been subjected to the pre-bending process, so as to completely bend the portion We (a main bending process or a final bending process).
If the portion to be processed has a large width, it is necessary to repeat the above-mentioned intermediate process two or more times.
As described above, according to the prior art, it is necessary to gradually process the portion We by roll-pressing the roller r0 against the portion We a number of times. Such a process takes a longer time compared to processes that use pressing dies (a pressing process using an upper die and a lower die).
It is, accordingly, an object of the present invention to provide methods and apparatus for roller type processing, which can reduce processing time and improve processing quality.
According to a preferred embodiment of the invention, a plurality of rollers are successively roll-pressed or in a close positional arrangement with respect to each other. Therefore, the workpiece can be gradually bent by the plurality of rollers in one pass. Thus, processing time can be significantly reduced. Further, the robot arms are controlled independently of each other, so that the rollers can be roll-pressed independently of each other without being affected by each other. Therefore, the rollers can be roll-pressed independently of each other even along a curved contour. Thus, this feature of the prior art roller type processing apparatus (i.e. processing along a desired contour) is not impaired.
The termxe2x80x9ccontinuously roll-pressing the rollersxe2x80x9d means that roll-pressing of one roller on the forward side in the rolling direction is followed by roll-pressing of another roller on the rear side in the rolling direction. In other words, a plurality of rollers are arranged in a line in the rolling direction (along linear and curved travelling paths) and are roll-pressed.
Further, during a process for bending an edge of a workpiece, in particular along a curved contour, a drawing process or extending process is locally performed, in addition to a so-called bending process. Therefore, in this specification, xe2x80x9cprocessingxe2x80x9d or xe2x80x9cprocessxe2x80x9d generally means a bending process, but it also includes drawing and extending processes that are performed when bending along a curved contour.
Further, the plurality of rollers are roll-pressed in rolling positions different from each other. Therefore, a pre-bending process and a main bending process (two kinds of processing), which for example are performed in a hemming operation, can be simultaneously performed. Thus, this kind of processing can be efficiently performed. In this respect, useful effects can be obtained that cannot be obtained by a processing apparatus in which a plurality of rollers are roll-pressed in the same positions, as disclosed in Japanese Patent No. 2579530, Japanese Laid-Open Utility Model Publication No. 61-122023 and Japanese Laid-Open Patent Publication No.2-112833.
The termxe2x80x9crollers having different rolling positionsxe2x80x9d means the state in which the orientation of each rotation axis of the plurality of rollers is different from each other.
In recent years, plates that are thinner than conventional plates have been increasingly used as the hemming material in hemming operations, in which the above-described processing apparatus and processing method are particularly suited. Conventionally, steel plates having a thickness of 0.8 mm to 0.7 mm have been typically used, but in recent years, considering vehicle safety and conservation of global resources, the trend in material thickness is to reduce the thickness by about 10 to 20%; thus, steel plates having a thickness of 0.65 mm to 0.6 mm are now typically used.
The reduction of the plate thickness has made it extremely difficult to obtain excellent results using the hemming operation. For thinner plates, deficiencies frequently occur, such as distortion or waving of the surface that has been processed, or waving of a flange portion. Therefore, it is extremely difficult to select processing conditions that can reduce or eliminate such deficiencies. For example, hemming devices as disclosed in Japanese Patent No. 2579530 and seaming devices as disclosed in Japanese Laid-Open Utility Model Publication No. 61-122023 and Japanese Laid-Open Patent Publication No.2-112833 can not achieve high-quality processing of materials having a complicated contour or reduction of processing time, both of which are required to hem such thinner plates. Specifically, the use of a plurality of robot arms as disclosed in the above publications only serves to widen the area that can be processed. Further, high-quality processing of a complicated contour cannot be performed by only continuously roll-pressing the rollers.
A preferred embodiment of the present invention can satisfy such high requirements, especially for hemming operations, such as complicated and high-quality processing and reduction of processing time, while improving productivity at the same time. Because the roller type processing apparatus and method according to the present invention have a plurality of rollers attached to a plurality of independently controllable robot arms, which are successively roll-pressed in respective rolling positions that are different from each other, the angular position, location and arrangement of each of the rollers can be set as desired.
According to another preferred embodiment of the present invention, before spring back occurs in a portion that has been processed by a preceding roller, a subsequent roller again processes the portion. Therefore, when processing, it is not necessary to compensate for spring back and processing can be achieved without distortions.
According to another preferred embodiment of the present invention, when the portion to be processed has a large width, one roller is roll-pressed along the proximal end of the portion, while the other roller is roll-pressed along the edge end of the portion. As a result, the wider portion to be processed can be processed in fewer cycles compared with the prior art.
According to another preferred embodiment of the present invention, the wider portion to be processed can be processed with higher accuracy in fewer cycles.
According to another preferred embodiment of the present invention, the rollers and the workpiece are simultaneously moved. Therefore, the rollers need not be moved from end to end of the portion to be processed. As a result, the actual working time of the robot arms and thus the processing time can be reduced.
Further, the workpiece portion to be processed positively moves toward the rollers. Therefore, parts of the workpiece portion to be processed that cannot be accessed purely by the movement of the robot arms (the movement of the rollers) can be also processed. Thus, the area that can be processed by the processing apparatus can be increased.